Anti-GBM antibody

Sample for Anti-GBM antibody

1. This test is done on the venous blood to get the serum.
2. The patient needs to fast for 8 hours.
3. Another sample is a tissue biopsy of the kidney and lung tissue. It is used for microscopic evaluation.

Purpose of the test (Indications) for Anti-GBM antibody

1. To diagnose autoimmune-induced glomerulonephritis.
2. To differentiate from the other type of glomerulonephritis.
3. To diagnose Goodpasture’s syndrome.

Precaution for Anti-GBM antibody

• Drugs like antibiotics may decrease the test result.

Pathophysiology of Anti-GBM glomerulonephritis

1. This is an autoimmune phenomenon.
   1. About 5% of glomerulonephritis is Anti-GBM type.
   2. Some autoantibodies react with the basement membrane of the renal glomeruli capillaries.
      1. These autoantibodies react with small blood vessels of the kidney and lung.
      2. These autoantibodies react with pulmonary alveoli.
   3. When these antibodies react only with the glomeruli basement, they produce anti-GBM glomerulonephritis.
   4. In Goodpastaur syndrome, there are circulating antibodies against the glomerular basement membrane. These antibodies also react against the alveoli of the lung.

The mechanism of the tissue damage:

1. It is a type III hypersensitivity reaction where immune complexes activate the complement system.
2. Immune complexes give rise to:
   1. Glomerulonephritis leads to hematuria.
   2. Pulmonary hemorrhage leads to hemoptysis.
   3. Positive autoantibodies against basement membranes.

3. This hypersensitivity reaction is complement-mediated.
   1. The damage is due to the deposition of immune complexes.

Goodpasture syndrome:

1. It is an autoimmune disease characterized by the following:
2. 1. When both kidneys and lungs are involved.
   2. Hematuria.
   3. Hemoptysis (pulmonary hemorrhage).
   4. Antibodies react to the kidneys and lungs’ basement membrane (antigen).
3. Both kidneys and lungs are involved in 60% to 70 % of cases (Goodpasture syndrome).
   1. 20% to 40 % of the cases show only involvement of the kidneys, only then called anti-GBM glomerulonephritis.
4. The patient will have blood in a cough when the lungs are involved.

Diagnosis of Anti-GBM glomerulonephritis and Goodpasture syndrome:

1. The serum method is easier, faster, and more reliable for patients with a difficult or contraindicated biopsy.
   1. Blood by enzyme immunoassay (EIA):
   2. Negative = <20 units
   3. Borderline  = 20 to 100 units
   4. Positive = >100 units
2. The high anti-GBM titer is suggestive of the following:
   1. Goodpasture’s syndrome.
   2. Lupus erythematosus.
   3. Anti-GBM nephritis.
3. Lung or renal biopsy demonstrates these antibodies by immunohistochemical technique.

Normal anti-GMB antibody

Source 2

Blood (EIA enzymatic immunoassay):

• Negative = <20 units.
• Borderline = 20 to 100 units.
• Positive = >100 units.

Tissue biopsy:

• Negative = No immunofluorescence was seen on renal or lung biopsy.

Source 4

• Negative = <5 EU/mL by ELIZA
• Borderline = 5.1 to 20.0 EU/mL
• Positive = 20.1 to 400 EU/mL
• A negative result does not rule out Goodpasture’s syndrome.

Anti-GBM antibody seen in:

1. Autoimmune glomerulonephritis.
2. Goodpasture’s syndrome.
3. Tubulointerstitial nephritis.
4. Some patients with lupus nephritis.

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